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SubjectKASAN: use-after-free Read in snd_ctl_elem_add
From
Hello,

syzbot found the following crash on:

HEAD commit: ccda4af0f4b9 Linux 4.20-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=139bbad5400000
kernel config: https://syzkaller.appspot.com/x/.config?x=4a0a89f12ca9b0f5
dashboard link: https://syzkaller.appspot.com/bug?extid=dc09047bce3820621ba2
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+dc09047bce3820621ba2@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in snd_ctl_get_ioff include/sound/control.h:164
[inline]
BUG: KASAN: use-after-free in snd_ctl_elem_add+0x1210/0x14d0
sound/core/control.c:1367
Read of size 4 at addr ffff8881780ba710 by task syz-executor1/10730

CPU: 0 PID: 10730 Comm: syz-executor1 Not tainted 4.20.0-rc2+ #112
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
snd_ctl_get_ioff include/sound/control.h:164 [inline]
snd_ctl_elem_add+0x1210/0x14d0 sound/core/control.c:1367
snd_ctl_elem_add_user+0xb8/0x170 sound/core/control.c:1392
snd_ctl_ioctl+0x480/0x1110 sound/core/control.c:1568
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe6bc8bac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
RDX: 0000000020000080 RSI: 00000000c1105517 RDI: 0000000000000006
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe6bc8bb6d4
R13: 00000000004c8a70 R14: 00000000004d15d8 R15: 00000000ffffffff

Allocated by task 10730:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3722 [inline]
__kmalloc+0x15b/0x760 mm/slab.c:3731
kmalloc include/linux/slab.h:551 [inline]
kzalloc include/linux/slab.h:741 [inline]
snd_ctl_new+0x5c/0x180 sound/core/control.c:223
snd_ctl_elem_add+0x555/0x14d0 sound/core/control.c:1324
snd_ctl_elem_add_user+0xb8/0x170 sound/core/control.c:1392
snd_ctl_ioctl+0x480/0x1110 sound/core/control.c:1568
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 10728:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3817
snd_ctl_free_one+0x5d/0x70 sound/core/control.c:313
snd_ctl_remove+0x43b/0x5a0 sound/core/control.c:504
snd_ctl_remove_user_ctl+0x17d/0x240 sound/core/control.c:568
snd_ctl_elem_remove sound/core/control.c:1410 [inline]
snd_ctl_ioctl+0xb25/0x1110 sound/core/control.c:1572
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881780ba6c0
which belongs to the cache kmalloc-16k of size 16384
The buggy address is located 80 bytes inside of
16384-byte region [ffff8881780ba6c0, ffff8881780be6c0)
The buggy address belongs to the page:
page:ffffea0005e02e00 count:1 mapcount:0 mapping:ffff8881da802200 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 ffffea00068ce008 ffff8881da801c48 ffff8881da802200
raw: 0000000000000000 ffff8881780ba6c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881780ba600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881780ba680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ffff8881780ba700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881780ba780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881780ba800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
kauditd_printk_skb: 174 callbacks suppressed
audit: type=1400 audit(1542205722.082:3119): avc: denied { map } for
pid=10761 comm="blkid" path="/lib/x86_64-linux-gnu/libblkid.so.1.1.0"
dev="sda1" ino=2825 scontext=system_u:system_r:kernel_t:s0
tcontext=system_u:object_r:file_t:s0 tclass=file permissive=1
audit: type=1400 audit(1542205722.102:3121): avc: denied { map } for
pid=10764 comm="modprobe" path="/lib/x86_64-linux-gnu/libkmod.so.2.1.3"
dev="sda1" ino=2811 scontext=system_u:system_r:kernel_t:s0
tcontext=system_u:object_r:file_t:s0 tclass=file permissive=1


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
syzbot.

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